The present invention relates to methods and devices for testing the effects of materials and surface coatings on encrustation and biofilm formation. More particularly, the present invention relates to methods and devices for testing the effects of various antimicrobial coatings on encrustation and biofilm formation on implantable medical devices.
Extensive study into the growth properties of microorganisms in recent years has shown that microorganisms form complex layers that adhere to surfaces. These complex forms of microorganisms are known as biofilms, or sessile microorganisms. Biofilms may cause problems in a variety of areas including the bodies of humans and animals, food processing, health care facilities and many other industries.
It is now known widely that microorganisms in the form of biofilms are more resistant to antimicrobial reagents than planktonic microorganisms. Yet traditional testing of antimicrobial reagents is performed utilizing planktonic microorganisms. Thus, the microbial inhibitory concentration of a reagent may be underestimated, with the result that the wrong antimicrobial reagent or wrong amount of antimicrobial reagent may be used for the treatment of microbial infection.
One type of device for monitoring biofilm buildup is described in the Canadian Journal of Microbiology (1981), Volume 27, pages 910-927, in which McCoy et al. describes the use of a so-called Robins device. The Robins device includes a tube through which water in a recycling circuit can flow. The tube has a plurality of ports within the tube wall, each port being provided with a removable stud, the stud having a biofoulable surface and being capable of being retained within the port in a fixed relationship with respect to the tube so that the biofoulable surface forms part of the internal surface of the tube. Each of the studs may be removed from the ports after a desired time interval and the surfaces analyzed for the growth of microorganisms. Alternatively, any surface growth may be removed and studied independent of the stud. The number of microorganism can be estimated for instance by physical or chemical means, e.g. by detection of bacterial ATP or by further culturing the microorganisms and analyzing the products.
Referring now to U.S. Pat. No. 5,349,874, Schapira, et al. there is shown another device for biofilm growth. Bacterial growth is determined in a water carrying conduit by providing a plurality of removable studs disposed within the conduit, or in a second conduit parallel to the first. The studs may be removed for analysis of biofilm growth on the studs. Such devices that utilize removable studs in a single conduit result in rather lengthy processing times and do not provide for rapid response times for testing of several different antimicrobial reagents.
In still another device which is described in Simple Method for Measuring the Antibiotic Concentration Required to Kill Adherent Bacteria, Miyake et al., Chemotherapy 1992; 38, 286-290, staphylococcus aureus cells adhered to the bottom of a 96 well plastic tissue culture plate were treated with serially diluted antibiotic solutions, viability of the cells were judged by their growth after a further 24 hours incubation. This method has the disadvantage of inconsistent colonization of sessile bacteria and settling of planktonic bacteria.
In addition to studying the formation of biofilms, there is great interest in the study of the formation of encrustation on implantable medical devices. Encrustation can be described as the formation of a foreign body on an implanted medical device. Examples of such encrustation are, calcium deposits, salt deposits, other mineral deposits, or the formation of thrombus or similar biological events. Each of the devices described above utilizes pins or similar protrusions to test the formation of biofilms thereon, a shortcoming of such a system is that they only provide an approximation of encrustation and biofilm formation. Thus, there is a need for a testing device that is configured to test various surface coatings on the formation of encrustation and biofilms on various medical devices or portions of medical devices.
It would be desirable to provide an apparatus and method for testing the effects of materials, such as surface coatings, on biofilm growth and encrustation formation and deposition. In addition, it would be desirable to provide an apparatus and method for testing the effects of materials on biofilm growth which provides rapid response times and the ability to test multiple materials or antimicrobial reagents or coatings at once.
In one aspect of the invention, there is provided a method for testing the performance of surface coatings on the formation of biofilm and encrustation on materials. The method includes, providing a plurality of material retaining sites, providing the material retaining sites with a material, wherein the material models a surface likely to be involved in biofilm formation and encrustation deposit. The method further includes the steps of providing a liquid growth medium, wherein the liquid growth medium includes at least one microorganism, the liquid growth medium arranged to cover at least a portion of the material, and incubating microorganism and encrustation on the material retaining sites in the presence of the liquid growth medium.
In another aspect of the invention, there is provided a method for testing the effect of materials and surface coatings on the formation of biofilms and encrustation in a controlled environment. The method including the steps of providing a plurality of biofilm and encrustation adherent sites, coating the biofilm adherent sites with a material which acts as a model for a surface likely to be involved in biofilm and encrustation formation, and providing a liquid growth medium arranged to flow across the biofilm and encrustation adherent sites. The method further includes agitating the liquid growth medium, growing microorganisms on the biofilm and encrustation adherent sites; and measuring biofilm formation growth and encrustation deposition on the material.